The invention relates to an arrangement for sealing foil covers onto packaging containers, particularly plastic cups by means of a heatable sealing head which supports a formatting part. This sealing head includes a driving mechanism for reciprocally moving the sealing head in the direction of the packaging container. The arrangement also includes a compensation mechanism which is mounted between the sealing head and the driving mechanism and which includes at least one thermal insulating element.
Sealing arrangements of the aforedescribed type are used in many ways in the packaging industry, e.g., they are used in conjunction with plastic cups or deep drawn packages which are sealed by means of aluminum foil covers. In such an arrangement, the sealing lacquer is applied to the aluminum foil, and the foil cover is, by means of pressure and heat, securely joined to the top edge so as to form a tightly sealed joint between the aluminum foil cover and the plastic cup edge. A flaw-free sealing and thereby a tight seal of the plastic cup, respectively deep-drawn package, is, however, only then provided when a uniform pressure distribution is present during the sealing operation.
This result can only be achieved when the sealing head, respectively the formatting member connected thereto, on the one hand, and the packaging container, respectively plastic cup, on the other hand, are precisely mutually aligned in the actuating direction as well as in elevation. These two parts must be mutually coordinated with each other. As a result of unavoidable dimension deviations with packages and plastic cups and the transport mechanism which feeds them to the sealing station, such as, e.g., a cellular sheet metal member or a round table, more or less large form and weight deviations occur, which, relative to the sealing head, must be compensated. A sealing arrangement, which has become well known in the art, provides for an axial compensation by means of a spherical head and a spherical cup which is arranged between the sealing means, on the one hand, and the driving mechanism on the other hand. Such an arrangement also includes prestressed springs arranged between the two parts that are to be actually compensated. The required elevation compensation is achieved with the coil springs mounted in the drive member. Such a compensation mechanism requires a total of nearly thirty individual parts, in order to furnish the required axial and elevation compensation. To this must be added that, despite the arrangement of a plurality of thermal insulating elements, a relatively high heat loss occurs by radiation from the sealing head which operates at a temperature of 280.degree. C. Thereby the spherical head and spherical cup are exposed to a relatively hot zone and are therefore highly thermally loaded. The incomplete thermal insulation between the sealing head and the drive mechanism requires also particular care during maintenance. It has been attempted to maintain the parts forming the assembly during the heating within supportable limits by means of water cooling. However, there is a relatively small constructional space available for such cooling, so that the cooling effect is limited. In no case is it possible, due to the required connection between the sealing head and the compensation mechanism, to provide an inner cooling of the sealing head